A hypothesis concerning a significant role played by monetary factors in the slowdown observed in the Polish economy after 2000 was formulated in the article. These factors include a shrinking monetary base and circulating cash resources. They appeared as a result to a coincidence of different circumstances, which - in a way perhaps partly unintended by the NBP (National Bank of Poland) - increased a restrictive character of the Polish monetary policy. The most important causes of changes in the analysed aggregates are considered to be effects of the sterilising operation, which accompanies the harmonisation of Polish obligatory reserves with those binding in the European Union. The next factor was the outflow of speculative capital in 1999 and 2000. A less significant cause was considered to be an increased demand for cash as a safeguard against the so-called problem of the year 2000. The NBP did not embark upon measures preventing a shock-like reduction of cash availability, which is the main means of payment in Polish conditions for many important sectors of our economy. The author presents a probable impact mechanism of these changes on the Polish economy. The analysis of 30- and 10-year time series for big groups of countries (including 56 and 82 countries, respectively) allowed to reject a hypothesis that shock-like changes in the monetary base are a very rare phenomenon and they can have harmful effects for the economy. Negative factors do not appear as long as reductions of the analysed aggregate result only from the reduction of reserves in the banking system. Further on, the analysis of comparable time series for 10 developed countries, 3 countries of Central Europe and the area of the European Monetary Union revealed that shock-like reductions of circulating cash volume are an extremely rare phenomenon. Central banks apparently avoid such situation. It was impossible to relate the analysed monetary shock with real changes due to a very limited number of events of this type. However, some data seem to indicate that they are related with a drop in economic growth rates and an increase of unemployment even in developed countries. Taking into account the structure and needs of the Polish economy the results of these studies are an additional confirmation of a research hypothesis linking a slowdown in the Polish economy with changes in circulating cash reserves. The impact of this factor was all the more acute as it coincided with an unfavourable business situation in the world economy and errors in the Polish fiscal policy.(original abstract)